Rhizobia symbiosis of seven leguminous species growing along Xindian riverbank of Northern Taiwan

Rhizobia symbiosis of seven leguminous species growing along Xindian riverbank of Northern Taiwan

Legume-rhizobia symbioses of seven leguminous species growing along Xindian riverbank of Northern Taiwan were investigated in this study. These legumes form either determinate or indeterminate types of root nodules. The determinate nodules of Alysicarpus vaginalis, Desmodium. triflorum, D. heterophyllum, Sesbania cannabina and the indeterminate nodules of Mimosa pudica harbored bacteroids of morphological uniformity (length of 1-3μm), while the indeterminate nodules of Crotalaria zanzibarica and Trifolium repens contained bacteroids of highly pleomorphism (size varying from 1 to 5μm). The enclosed bacteria were isolated from respective nodules, and twenty slow-growing and nine fast-growing rhizobial isolates were recovered. The slow-growing isolates were classified to the genus Bradyrhizobium based on the 16S rRNA sequences, whereas the fast-growing rhizobia comprise four genera, Neorhizobium, Rhizobium, Cupriavidus and Paraburkholderia. Results of stable isotope analyses revealed that the seven leguminous species had similar and consistently negativeδ15N values in leaves (mean of -1.2‰), whereas the values were positive (varying from 3.7 to 7.3‰) in the nodules. These values were significantly higher in the indeterminate nodules than those in the determinate ones. In addition, variations in the values of leafδ13C (varying from -29 to -34‰) among the seven legumes were measured, indicating their photosynthetic water use efficiencies were different. This is the first field survey to report the rhizobial diversity and the nutrient relationships of sympatric legume in Taiwan.